Questions

  • is it okay to use the mean value across the admin1?

To do

  • Look at each month separately
  • heat map with co-occurence dry spells instead of below monthly precip

Background

This document explores the skill of ECMWF’s seasonal forecast, to predict dry spells. Bladiebla Have leadtime 1 to 6, where 1 is the month the forecast was released. However, forecast only released on 13th of the month.

Definitions

This analysis

  • Only looks at the Southern region since almost all historical dry spells occurred in that region
  • Only looks at the months of December, January, February since these months the crops are most sensitive to dry spells
  • Computes the monthly precipitation as the mean value of all cells within the admin1

What is the percentage of ensemble members forecasted below a certain threshold?

The figure below shows for how many months the % of ensemble members was below 180 mm. The 180 mm was the threshold set based on overlap of dry spells and monthly precipitation analysis.

We can see that the number of months lowers as the percentage increases, which is expected. While patterns differ slightly between lead times, the pattern is rather similair.

To set the threshold of % of members, we look at the observed data and count how many months had <=180mm. This were 21 months. We then choose the % for each leadtime which has closest to 21 months forecasted <= 180mm

What is the miss and false alarm rate per leadtime?

After setting the % of members, we get a list of forecasted months for which we would have triggered. Now we can compare these with the observed months with less than 180 mm of precipitation.

Heatmaps (ugly)